This unit supports what the kids have already read or learned about simple machines and gives them the opportunity to try out different things for themselves. Just as importantly, it introduces or reinforces experimental technique and scientific thought: things like hypotheses, conclusions, deductions, predictions, applications, observations, documentation and data analysis. It also makes heavy use of language arts and math skills and provides an opportunity to reinforce teamwork skills.
The unit is laid out for the kids to work in teams of two (or three if there's an odd number of students). It's important to stress that in experimental science, there is no "right answer". If you've done the experiment correctly and recorded your (not your neighbor's) results, you've got the "right answer" even if it's different from the rest of the world. I always encourage kids to compare their answers with what they expect and with what other teams observe. If there are major differences, it may be appropriate to repeat the experiment or try to figure out why. But there observations are still correct. As an example, one third grade student insisted, based on his observations with a compass, that north was in a direction which everyone else thought was east. It turns out that his desk was magnetized so, for him, the compass really did point in a different direction. It was probably beyond the abilities of a third grader to figure out why this was happening but it was important that he duly recorded his own observations, however peculiar they seemed.
If you are going to do the two experiments at different times, have the kids write their names on the index card marker and keep it for use in the second experiment.
The paper clips are used as "hooks" in the experiments so the kids inevitably want to open them up into an "S" shape. They are stronger if they are left closed. Machines At Home Notes Springs can be the standard helix or they can be flat metal or plastic (e.g., leaf springs in some car's suspensions). Some possible springs are on electric can openers, computer keyboard keys, storm doors, mechanical clocks, clothes pins, safety pins, paper clips (the kind you squeeze to open), bicycle seats, and in box springs or upholstered furniture.
The harder two objects are squeezed together, the more friction there is between them. Gravity is "squeezing" the book(s) against the desk. The more books, the more weight, the tighter they are squeezed against the desk, the more friction.
Friction 2: In general, rough, bumpy surfaces will have more friction. The wax paper may have more OR less friction than the bare desk depending on the surface of the desk and the brand of wax paper. This is a good opportunity to stress the importance of making your own observations rather than trying to guess the right answer. If different teams get different results, it might be interesting to have the teams compare their techniques, develop a hypothesis about why the results were different, and test it.
Overcoming Friction 1: Using rollers, the kids should only need a single weight to move 1 or 2 books. Clearly the wheel has its advantages. This provides a lead in to the next section on wheels since rollers are just wheels that are not attached to the object they are moving.
Overcoming Friction 2: The energy from friction is converted into heat energy. Their hands should get hot. They might try to observe the variables involved and how changing them makes their hands hotter. The two I have in mind are how tightly they squeeze their hands and how briskly the rub them. If you don't have hand lotion, liquid soap or even water works as well. Machines At Home Notes Like gravity, friction is neither always good or always bad. Wheels will not roll without friction - they just slip. Snow tires have deeper treads and even spikes to increase the amount of friction the tires experience while snow, ice and water all tend to reduce the friction. On the other hand, friction between the moving parts in your car's engine can be a very bad thing, especially if you have a leak in your cooling system. The energy from friction is turned into heat. There can be so much friction in your engine that it can, if not properly cooled, create enough heat to destroy the engine.
Pulleys 1: Pulleys can help us by making it easier to lift things or lower them. They can also redirect forces. For example, You might pull the rope horizontally as in Pulleys 2 but the load is still lifted up. Pulleys also let us move loads in places we might otherwise not be able to. For example, it would be difficult to stand on the top of a flag pole and pull the flag up. But using a pulley allows us to stay safely on the ground.
Pulleys 2: This experiment introduces the very important concept of conservation of energy: if you exert less energy, the job is easier but less work will be done. This is shown here and later on in levers in that fewer weights are needed to lift the load but it doesn't go as high.
By the way, three pulleys makes the job even easier that two.
Gears 1: An introduction to gears and terminology. Let the kids get familiar with how to set them up and use them. The focus is on the direction of rotation. Give the kids a chance to analyze their data and deduce the fact that whether or not the follower turns in the same direction as the driver depends only on if there's an odd or even number of gears in between.
The kids are asked to make a prediction which they should certainly test. Presumably they will find that their rule applies independent of the size of the gears.
Gears 2: In this experiment, we look at the speed of gears of different sizes and derive the concept that, regardless of size or shape, if the driver turns the distance of one tooth, the adjacent gear will also move exactly one tooth. So, if the driver has 20 teeth (small gear) and the follower 40 (medium gear), you must turn the driver two times around (20 + 20 teeth) to get the follower to turn one time around.
There's another chance in this experiment to analyze data graphically, to deduce the rule being followed and then apply the rule to a new situation.
Gears 3: There are so many types of gears and gear combinations. This experiment introduces the crown gear and a real application of what the kids have learned. They get to design their own machine and then build it.
Challenge: Since the driver and the follower have the same number of teeth in each of these drawings, it doesn't matter what is in between. The follower will always turn one time. The direction of rotation changes, but we didn't ask about that.
Machines At Home Notes There's the tires, steering wheel, lots of wheels in the engine, and knobs galore on the dashboard.
If you use rulers, they have to be the thick wooden kind that won't bend under these loads. There are flat sticks in the kit to use in place of rulers. You must use hexagonal pencils; the lever tends to roll off of the round ones thereby changing the results.
Machines At Home Notes: This one is fun to do in the classroom where all of the kids are looking at the same set of objects. Levers include water faucet handles, the handles on the windows, the paper cutter, scissors, stapler, and, often overlooked, the pull-tab on zippers. Can the kids identify the fulcrum, load and force for any of these?
Inclined Plane 1: The whole purpose here is for the kids to see that a screw is a type of inclined plane. We start with what is obviously an inclined plane and turn it into a screw. In the case of a screw (an inclined plane wrapped around a rod or axle), the rotational motion (let's say horizontal) results in linear motion (vertical).
Inclined Plane 2: Wedges are another very common form of inclined plane. They look more like an inclined plane. But many things are wedges that we don't recognize as such. Knives for instance. Look at the blade of a knife from the end (it's cross section) and it looks like a wedge. If you think about it, you push down (vertically) on the knife and the butter (or whatever) spreads apart into two pieces (horizontally).
Challenge: The knife is explained above. All of the items on the list are inclined planes.
Machines At Home Notes: Most screws are "right-hand" screws. They turn counterclockwise to open. The one notable exception that we probably all have come across is the left pedal on a bicycle. It is a "left-hand" screw. Otherwise, the pedal would unscrew as you were riding.
The term "right-hand screw" comes about because if you curl the fingers of your right hand in the direction the screw is turning, your thumb will point in the direction the object will move.